The home side began the match determined to overturn their 1-2 deficit from the first leg of the final, but it was the visitors who struck first, with midfielder Pham Tuan Hai scoring an early goal to add on the pressure.
Tuan Hai cleverly lobbed the ball past Thai goalkeeper Patiwat Khammai in the eighth minute, silencing the hostile crowd at the Rajamangala Stadium.
Following Tuan Hai's goal, Thailand intensified their attack and created several chances through midfielders Suphanat Mueanta and Benjamin James Davis.
The pressure paid off momentarilly as Thailand's equalizer came in the 28th minute after a mistake by a Vietnamese defender, who passed the ball directly into the path of Davis. The Thai midfielder skillfully curled the ball past Vietnam goalkeeper Nguyen Dinh Trieu.
However, Vietnam's prolific striker Rafaelson Fernandes, also known as Nguyen Xuan Son, had a disappointing evening as he was stretchered off the pitch due to a leg injury, prematurely ending his game in the 33th minute.
Both teams adopted a more cautious approach in the second half, but Thailand's Supachok Sarachat curled a stunning goal in the 64th minute to level the aggregate score.
However, the night did not belong to the hosts as Thailand was reduced to 10 men after Weerathep Pomphun received his second yellow card in the 74th minute.
Vietnam capitalized on their numerical advantage, creating several opportunities that culminated in an own goal by Thai defender Pansa Hemviboon in the 82nd minute.
The Golden Dragons sealed the victory in extra time when Nguyen Hai Long slotted the ball into an empty net after Thailand had pushed all their players forward in a desperate attack.
-- BERNAMA